There should be diversity between different classes, since its how TF2 is supposed to be. By making all the same classes have equal health and speeds, its gonna make certain classes completely useless. Whips cannot insta-kill (sadge) if that happens. Also not to mention, certain classes can...
Its favortised towards classes that can easily rebel, I.E: Scout, Spy. It means that they can easily rebel without the fear of losing 90% of their health.